1. Field of the Invention
This invention generally relates to the fabrication of integrated circuit (IC) devices, and more particularly, to a deposition oxide interface with improved oxygen bonding and a method for forming the same oxide interface using high-density plasma.
2. Description of the Related Art
FIG. 1 is a schematic of a stacked gate structure for a thin film transistor (TFT) (prior art). The proper performance of devices employing an oxide interface depends, in part, on the characteristics of the oxide interface within the device structure. A TFT using silicon oxide is presented as an illustration, however, it is understood that the discussion applies to other IC devices and to other types of oxides as well. In FIG. 1, oxide layers form the gate insulator. The bulk, or physical, characteristics and the interface, or electrical, characteristics of the gate insulator are very important for the operation of a TFT. Silicon dioxide (SiO2) is a suitable dielectric for the fabrication of TFTs because of its excellent micro structural and electrical characteristics.
Typically, conventional fabrication and post-depositional processing of SiO2 thin films are performed at temperatures greater than 400° C. hereafter referred to as high temperatures. High temperatures are used to enhance bulk and interface characteristics for device applications and to attain economically feasible rates of production. However, even at high temperatures, the quality of silicon oxide generated by a conventional deposition process, such as plasma enhanced chemical vapor deposition (PECVD), is degraded by incomplete oxidation, impurity bonding, non-stoichiometric oxide bonding, and low density. Incomplete oxidation causes a percentage of silicon oxides in the oxide layer to take the form SiOx, where x is less than 2. Impurity bonding results in the formation of undesirable compounds such as SiOH or SiH in the oxide. The impurities in these compounds, for example hydrogen, are typically derived from a precursor used as part of the deposition process. Non-stoichiometric SiO2 is formed when the deposition process does not supply sufficient energy for SiO2 produced by the process to reach equilibrium. SiOx, non-stoichiometric SiO2, and impurity compounds produce an undesired reduction in oxide layer density and adversely affect oxide layer bulk and interface characteristics.
The next generation of higher density display devices, such as liquid crystal displays (LCDs), requires high performance TFT driver components processed at temperatures less than 400° C., hereafter referred to as low temperatures. Processing TFT components at low temperatures enables the integration of oxide films on glass, plastic, and other low temperature substrates. These low temperature substrates can be used to fabricate high performance, high resolution, thin, lightweight, low-power displays. Further, a process temperature in the range of 100-300° C. does not damage transparent and flexible plastic substrates. A conventional deposition process, such as PECVD, can be performed at low temperatures. Unfortunately, performing conventional deposition processes at low temperatures exacerbates the oxide quality problems noted above and results in lower oxide deposition rates. In addition, increasing power or other processing variables at low temperatures to enhance deposition rates leads to interface damage and other problems resulting in lower interface quality.
It would be advantageous if a low temperature process could improve the bulk and interfacial properties of a deposition oxide.
It would be advantageous if a process could effectively oxidize a deposition oxide film regardless of a substrate temperature.